bench: update random value generation

[hrshya]

Resolves none .

Description

What is the purpose of this pull request?

This pull request:

• Refactors random number generation in JS benchmarks for the math/base/special/gamma and math/base/special/gamma-delta-ratio packages.
• Replaces randu() with uniform() from @stdlib/random/array/uniform for cleaner and more consistent code.
• Moves the random number generation outside the benchmarking loops.
• Updates the test messages to follow code conventions.

Related Issues

Does this pull request have any related issues?

This pull request:

• resolves no related issues.

Questions

Any questions for reviewers of this pull request?

No.

Other

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No.

Checklist

Please ensure the following tasks are completed before submitting this pull request.

• Read, understood, and followed the contributing guidelines.

---

@stdlib-js/reviewers

[stdlib-bot]

Coverage Report

Package	Statements	Branches	Functions	Lines
math/base/special/gamma-delta-ratio	$339/341$ $+99.41\mathrm{\%}$	$32/33$ $+96.97\mathrm{\%}$	$3/3$ $+100.00\mathrm{\%}$	$339/341$ $+99.41\mathrm{\%}$
math/base/special/gamma	$547/556$ $+98.38\mathrm{\%}$	$48/52$ $+92.31\mathrm{\%}$	$6/6$ $+100.00\mathrm{\%}$	$547/556$ $+98.38\mathrm{\%}$

The above coverage report was generated for the changes in this PR.

[kgryte]

LGTM